First timer to CNC with a few questions

[frostyshoal]

I've been working on Joe's CNC plans for a few weeks now, just finished cutting all the wooden parts out tonight and assembling it, only thing left is to get the electronics and bearings come in the mail tomorrow. Posting here instead of in the Joe forum because my questions are more general though. I have tried searching for all these answers but am starting to get frustrated, this forum has so much info its hard (at least for me) to find the info I need.

1. What type of drill bit should I use on the router? I will be cutting wood, MDF and possibly plastics, simple machine parts, and possibly some 3d shapes. I found this bit of info "Remember: UPCUT bits provide fast chip ejection and deliver the finest finish on the lower surface of the workpiece. DOWNCUT are the best choice where an ultra-smooth finish on the upper surface is the highest priority." I don't get what it means by upper or lower

2. I don't have the electronic components yet, but I'm wondering how exactly how do you calibrate the machine, basically how it will know where it is and how far it moves etc?

3. Can I sell things I make with this machine or do I need special license besides the software ones?

Thanks

[apache405]

1. What type of drill bit should I use on the router? I will be cutting wood, MDF and possibly plastics, simple machine parts, and possibly some 3d shapes. I found this bit of info "Remember: UPCUT bits provide fast chip ejection and deliver the finest finish on the lower surface of the workpiece. DOWNCUT are the best choice where an ultra-smooth finish on the upper surface is the highest priority." I don't get what it means by upper or lower

I think you mean end mills, not drill bits.

To answer your question with a diagram.
Imagine the region of "=" as the part you are cutting.
I labeled where the upper and lower are.

=========== (Upper)
===========
===========
=========== (Lower)
====================
====================
====================

2. I don't have the electronic components yet, but I'm wondering how exactly how do you calibrate the machine, basically how it will know where it is and how far it moves etc?

I can answer the how the machine makes an educated guess about the position of the cutting head.

If you are using stepper motors, then the following is true:

The motor moves a know amount for every step it is given. When your computer give a step command to the motor, it contains 2 things: a direction (polarity of the step, if memory serves) and a pulse (the actual step).

The last robot I built had 1.8 degree/step motors in it. This means that every 200 steps you get a full 360 degree revolution.

The screw mechanism in the machine converts the rotation into a linear distance. The quick explanation is your screws have a TPI or threads per inch rating, for example, let's say 8 TPI. That means for every 8 revolutions your motor makes, the screw will move the nut 1" (ideally). In reality there is an equation that the controller uses to calculate the position, but it is subject to some assumptions, which breakdown if the machine skips steps.

3. Can I sell things I make with this machine or do I need special license besides the software ones?

Yes, I see no reason why not. There is usually some annoying paperwork to deal with though, if you want to be 100% compliant with the law (i.e. tax nonsense, business license, etc.). But while you are starting out, and making a little bit here and there, don't worry about it. Consult your city's administration if you want to know all of the ins and outs. I know San Diego has an office for small business assistance, but I don't know about where you live.

Hope that helps...

[jalessi]

Frosty,

Home and limit switches really help.

http://tinyurl.com/lejrqh

Watch this video for axis calibration.

"http://www.youtube.com/watch?v=XkO5tc-jSxw&feature=channel_page"]YouTube - Improved Mach 3 Axis Calibration

No special software license is required to sell what you make.

Local or state laws may require you to have a business license.

See this site for router bit tool selection.

http://www.ekstromcutter.com/ToolSelectionGuide.htm

Jeff...

[Hirudin]

I can help a lil' with #2 and #3...

2a - How it will know where it is...
For this you'll use some kind of "edge finder" or "center finder". There are several different kinds: mechanical, electronic, laser, optical, and probably some that I haven't ever heard of. Some videos...
"http://www.youtube.com/watch?v=f0od-cp_9dg"]YouTube - Using an Edge Finder - Tormach CNC < dig that music!
"http://www.youtube.com/watch?v=Oc-9gTFj-y4"]YouTube - Laser Zero finder
Laser 2 < WMV file
"http://www.youtube.com/watch?v=KOXY4O0UkRM"]YouTube - Mach3 CNC Probe Tool
There is another kind of optical edge/center finder that I guess is a little like a rifle scope - you stick the reticle exactly where you want to set the machine to zero.

I think the reticle type optical edge finder is the most accurate, the electectronic type gives very good accuracy and aren't too expensive, and the kind in the first laser video is probably the quickest and easiest.


2b - How does the machine know how far it's moved... (sorry if you already know all this, I figured I'd just write a simple explanation)
This is simple math for the most part. If you're using screws with 10 turns per inch than you know it'll take 10 turns for the machine to move 1 inch. If you turn the screw 1 time it'll move 1/10 (or 0.1) of an inch. Quarter of a turn will move the machine 0.025 inches.

The computer can turn the motors very precisely and therefor can move the machine very precisely. If you're using stepper motors the computer knows where the machine is simply by knowing how many times each of the motors has turned.

To improve the accuracy even more you will want to set the "steps per inch" using a technique like in "http://www.youtube.com/watch?v=XkO5tc-jSxw"]YouTube - Improved Mach 3 Axis Calibration. For a very large machine like Joe's this might not be very critical, I'm not sure.

3. I'm not a big city lawyer (or any other kind of lawyer) but I'm very sure you can sell original creations cut with your machine. I imagine you could only run into legal trouble by cutting out someone else's design without their permission.
... Oh, and the business license stuff as the people above me said.

[barry wetherell]

HI, guys, seems to be back to front to me, ... I would think that the "latest post" be the first thread one would see, or perhaps, it's me.
Anyway, the reason for being a member is that, I am trying to come to grips with all of these "thingys" that requires one to build one of these units.
I am a model aircraft builder, and have been since I was 11, I am now 60, so I have no problems about constucting the unit.
here is what I would would like my unit to.
1:- transfer a "plan" onto a cad program
2:- transfer this onto the router and cut out wing rib profiles and fusalage formers
sounds simple to me. this is what i have
3 x nemo 17 biplor stepper moters
drawings for the unit
Mack 2/3 program
other assorted cad programs
most of the requirements to build the XYZ units + a Dremal motor
so there you are WHAT is next, and where do I get it in Aus, ??????????????? Help pleaseI live in Port Hedland WA. Thanks Barry

[apache405]

Barry,

The latest post last thing is the default for the forum, there is a way to change it somewhere in the user prefs section. It's done that way so that the reader sees the evolution of the thread and get the full context of the thread.

In your case, I would check out the stuff widgetmaster has made. I believe he sells the machine he designed, and that sounds like the right size for you (I'm assuming that your parts are about 10x5" max. His machine should run with a Dremel sized tool as the spindle. Be forewarned the Dremel has nasty TIR problems.

I think NEMA 17's should be fine for your application, but it will be slow. Mach 3 is a really good choice for controlling your machine, however you will want to stay away from Windows XP service pack 3 on the computer your put Mach on. There is appratnely some type of execution delay designed to foil malware and other evil programs, but it also messes up Mach.

In terms of getting your parts, look at the ads here and look at other people's build logs. They usually post links to the places where they got their parts from.

The other thing you can do is make your CAD drawings and then pay a shop with a CNC laser cutter (also called a laser CAM) to make your parts.

If you need further help with hammering out the details of your machine, you should probably start a fresh thread, so you don't hijack frostyshoal's thread.

[barry wetherell]

Thank you Jeff, I live in Aus

[barry wetherell]

Jeff, Widgetmaster....????